As a substrate processing apparatus for carrying out one step of a manufacturing process of a semiconductor device (a device), there is a vertical CVD apparatus which performs processing such as film forming for a large number of wafers in a reaction chamber (hereinafter, also referred to as “in a furnace”). In the conventional vertical CVD apparatus, in the semiconductor manufacturing process, in particular, when the reaction chamber is opened, particles scatter from a particle generation source into the furnace, and the particles are prone to be adhered onto a surface of each wafer. The particle generation source is a reaction product adsorbed on a reaction chamber wall, a pipe wall, or the like. The film forming is repeated in the furnace, films of the reaction product are thereby adsorbed on the reaction chamber wall, the pipe wall, or the like, and the films are exfoliated and become particles 92 as shown in FIG. 8. For example, when film forming of a silicon nitride film (a SiN film) is repeated, Si3N4 films 90 are deposited on the wall surfaces in a high temperature region of 500° C. or more, and ammonium chloride films (NH4Cl films) 91 are deposited thereon in a low temperature region of 150° C. or less, and these are exfoliated and become the particles 92.
At the time of the film forming step, in FIG. 8, if places on which the Si3N4 films 90 are prone to be adsorbed are first mentioned, the places are a surface of a quartz-made boat 117, and an inner wall of an inner reaction tube 104 which constructs a quarts-made reaction pipe (hereinafter, also referred to as a “furnace body”) 103 with a double-pipe structure, on an outer circumference of which a heater 102 is provided. If places on which the NH4Cl films 91 are prone to be adhered are mentioned next, the places are a lower outer wall of the inner reaction tube 104 in the vicinity of an exhaust port 111, an inner wall of a metal-made, for example, stainless steel-made manifold 106 to which a supply pipe 132 and an exhaust pipe 112 are connected, an inner wall of the supply pipe 132 which introduces reaction gas into the reaction chamber, an inner wall of the exhaust pipe 112 connected to the exhaust port 111 of the manifold 106, an inner wall of a seal cap 119 which seals a throat opening 116, and the like.
Owing to a fact that the film forming is repeated in the furnace, the Si3N4 films 90 are deposited on the high temperature regions of the above-described members, and the NH4Cl films 91 are deposited on the low temperature regions thereof. When the Si3N4 films 90 deposited in the reaction chamber 101 and the NH4Cl films 91 deposited on the low temperature regions of the reaction chamber, the manifold, and the pipes are exfoliated, these films become the particles 92. Note that, in the drawing, the SiN (Si3N4 films) 90, the NH4Cl films 91, and the particles 92 are drawn emphatically for the sake of convenience.
When the films adsorbed and deposited on the wall surfaces are exfoliated from the wall surfaces owing to some cause, the films become the particles 92. A description will be made of a generation mechanism of the particles by using FIG. 9.
FIG. 9 shows a step (a wafer loading step) of elevating (boat up) the boat 117 having the wafers 100 charged thereon in a direction of an open arrow, and loading the wafers 100 into the reaction chamber 101. When the throat opening 116 is opened, heat radiation from the throat opening 116 toward the outside occurs, and temperature of the furnace body drops.
Moreover, since the wafers 100 and the boat 117, which are at room temperature, are loaded into the reaction chamber 101, temperature of the wall surface of the heated reaction pipe 103 is lowered. Accordingly, the SiN films 90 adhered onto the wall surface of the reaction pipe, and the like, undergo a stress caused by a difference thereof in thermal expansion from the reaction pipe 103, and are exfoliated from the wall surface, and the particles 92 are generated.
Furthermore, also in a (wafer unloading) step of lowering the boat 117 which holds the already processed wafers 100, and unloading the wafers 100 from the reaction chamber 101, the particles are generated owing to a similar mechanism to the above. It is conceived that the particles are generated because of the following reason. Specifically, since the wall surface of the reaction pipe and the manifold are going to be exposed to the outside in a pipe axial direction by the high temperature portion of the boat when the wafers 100 and the boat 117 are unloaded from the reaction chamber 101, in particular, the NH4Cl films 91 adsorbed on the wall surface of a lower portion of the reaction pipe and an inner wall surface of the manifold, which become the low temperature regions, undergo a stress, and are exfoliated from the wall surfaces, and the particles 92 are generated.
In this connection, in order to prevent contamination of the wafers by the above-described particles, heretofore, there have been proposed a method of back-purging and slowly exhausting the reaction chamber at the times of wafer loading/wafer unloading (for example, refer to Patent Document 1), and a method of introducing inert gas into the reaction chamber and slowly exhausting the reaction chamber in a state where the reaction chamber is opened (for example, refer to Patent Document 2).
Patent Document 1: Japanese Patent Laid-Open Publication No. H10-326752 (published in 1998)
Patent Document 2: Japanese Patent Laid-Open Publication No. H8-31743 (published in 1996)